1. Field of the Invention
The present invention relates to a diagnostic method and apparatus for a vehicle for diagnosing the conditions of various component parts mounted on a vehicle and, more particularly, to a diagnostic apparatus for a vehicle which can transmit diagnosis results to a management center on the outside.
2. Related Art
Maintenance of a vehicle is controlled in such a manner that, for example, in Japan, the user asks a maintenance shop to inspect and repair a vehicle in accordance with a vehicle inspection of every predetermined period and reports the result to the district land transport bureau. In U.S.A., the user asks a maintenance shop to inspect and repair a vehicle in accordance with a periodic notification from the competent bureau and sends the result indicating that the requirements are satisfied to the competent bureau.
In such methods, a vehicle having no trouble and defect which requires no maintenance is uniformly managed. Consequently, the man-hour of the management in the competent bureau (the district land transport bureau) is long and it is also troublesome for the user.
It is therefore considered that information regarding the inspection (for instance, information regarding an abnormal engine-related parts) on the vehicle side is transmitted from the vehicle to the competent bureau by radio communication and the competent bureau instructs the user of the vehicle which requires a repair to report.
In case of constructing such a system, it is necessary to construct that the vehicle side is equipped with an apparatus for transferring and receiving information by radio (transponder) and information regarding an inspection is obtained by a control unit mounted on the vehicle and is sent from the control unit to the transponder.
When the transponder which has received a transmission request from the competent bureau side sends a request to output the information regarding the inspection to the control unit, however, if the request timing is at the same time with engine starting time, the communication state at that time is busy. There is consequently the possibility that noises occur on a communication line between the transponder and the control unit, for example, a signal which is inputted to the transponder is likely to differ from a signal generated from the control unit and erroneous information is likely to be sent to the competent bureau. When a microcomputer of the control unit is busy, for example, in case of an engine control unit, if an output data amount to the transponder increases when the engine speed is high or a load is high (in the case where the control unit detects and stores an abnormality), it is likely that an inherent control process is influenced.
Even when the control unit does not respond to the output request from the transponder but the control unit itself requests to output a diagnostic result, for example, at a predetermined timing of outputting the diagnostic result, the above inconvenience at the engine starting time and the busy time of the microcomputer of the control unit similarly occurs.